Helmets, Concussions, and Risk Compensation

This month's issue of the British Journal of Sports Medicine is devoted to the results of a big conference on concussion held last November in Zurich. The consensus statement they agreed on is free to read at the BJSM site. There are lots of interesting tidbits, given the recent focus on head injuries in the media; for example, they note that "the speculation that repeated concussion or subconcussive impacts cause CTE [chronic traumatic encephalophy] remains unproven." This seems awfully cautious given the mounting circumstantial evidence, but I guess the role of science is to proceed cautiously.

Anyway, the bit that caught my eye was on helmets and the idea of "risk compensation." A few years ago, I wrote some blog posts about the arguments for and against bicycle helmet use, and I was totally bowled over by vehemence of the response from people on both sides of the debate (which, I like to think, indicates that I had a balanced take!). Here's what the new concussion consensus statement says:

There is no good clinical evidence that currently available protective equipment will prevent concussion... Biomechanical studies have shown a reduction in impact forces to the brain with the use of head gear and helmets, but these findings have not been translated to show a reduction in concussion incidence.

Note, however, that head and face protection do seem to reduce dental and facial injuries, as well as serious outcomes like skull fractures. And on the topic of risk compensation:

This is where the use of protective equipment results in behavioural change such as the adoption of more dangerous playing techniques, which can result in a paradoxical increase in injury rates.

Having spent the last few years in Australia watching AFL players absolutely bludgeon each other wearing nothing more than a T-shirt and a pair of Daisy Dukes (or "stubbies," as they're known Down Under), I've often wondered whether introducing helmets would make them safer, or would simply transform the sport into a version of American football with even higher impact forces directed -- via the helmet -- at the brain. This is essentially the same debate that exists with cycling: does wearing a helmet make you feel safer, and thus encourage you to ride faster and end up with roughly the same level of injury risk?

There have been plenty of studies of this question, but the results are often difficult to interpret -- so the results coincidentally always seem to support whatever hypothesis the authors start with. For example, a new Norwegian study in Accident Analysis & Prevention took a bunch of volunteers and had them cycle down a gentle hill with and without helmets. Habitual helmet-wearers slowed down (by a non-significant amount) when they were asked to cycle without their helmets; habitual non-wearers didn't change their speed when they put a helmet on. You could interpret this as evidence that making people wear helmets doesn't make them speed up. But the authors look at it the other way around: since the helmet wearers slow down without their helmets, this proves that there is some form of risk compensation going on!

I don't doubt that risk compensation exists, but I do doubt that it's a "perfect" mechanism that fully resets risk to the same level. Seat belts are a prime example: yes, you likely drive marginally more recklessly with a seat belt on, but the statistics are clear that you still end up much safer overall. Moreover, for generations that grew up after that debate ended, I think the compensation effect is far weaker. When I grew up, the idea of getting into a car without putting on your seat belt would never have been considered, so I've never felt any feeling of "extra" safety from wearing a seat belt -- just like knowing that my car has a bumper and a shatter-proof windshield doesn't make me drive more recklessly!

Of course, there are plenty of other arguments in the cycling debate -- for example, that forcing people to wear helmets will decrease the overall number of cyclists, consequently making it harder to get approval for dedicated cycle lanes and other infrastructure, and ultimately resulting in a less safe environment for those who continue to cycle. This argument, to me, is much more powerful than the simple risk compensation argument. From a legislative point of view, I see both sides of the argument and don't know which is the better approach. From a personal point of view, I wear a helmet and don't have even a millisecond of doubt about the decision.